1. Field Of The Invention
This invention relates generally to the field of paint rollers and, more specifically, a method of and apparatus for making a paint roller with a thermoplastic core in a continuous, low cost production method. The final product is a paint roller of the type described in U.S. Pat. No. 5,206,968 in which the pile fabric cover is bonded directly to a thermoplastic core, the core having been formed and the pile fabric applied in a continuous, uninterrupted sequence of processing steps.
2. Background Of The Invention
Two methods of manufacturing pile fabric paint rollers on thermoplastic cores are currently widely used, which methods result in dissimilar, though usable products.
In the first method adhesive is applied to a previously extruded core blank and thereafter pile fabric in strip form is wrapped around the adhesive carrying core blank. After setting of the adhesive, or at least the formation of a good bond between the pile fabric and the adhesive, the core blank is cut into pieces of the desired length which may or may not be further processed, as by trimming the end edges of the pile fabric. This system has several disadvantages including (a) substantial expense and considerable complexity, with the resultant opportunity for production interruption, due to the use of three components--core, adhesive and pile fabric--as contrasted to use of only two components--core and pile fabric, (b) substantial scrap loss due to the need to use preformed, hardened cores of discrete length with consequent wastage at each end, (c) high operating costs in addition to those mentioned earlier if a pre-extruded and cooled core containing no residual heat is reheated to assist in adhesive application, (d) substantial inventory costs associated with stocking preformed cores, and (e) limitation of the resultant roller cover products to organic paint solvents. Controlling the optimum processing characteristics of the adhesive and the specialized equipment for its application can be particularly troublesome.
In the second method, exemplified by U.S. Pat. No. 4,692,975, pile fabric formed with a thermoplastic backing material is applied directly to a compatible thermoplastic core blank, and the use of adhesive with its associated cost and operating drawbacks is thereby eliminated. The elimination of adhesive is a distinct advantage because the thermoplastic materials commonly used have good resistance to paint solvents in contrast to the lesser resistance of components which have been used in the adhesive systems, i.e., thermoplastic materials which can be glued to generally have poor paint solvent resistance. Although this system is a distinct advantage over adhesive type systems, optimum results are not always achieved due to the discontinuous nature of the process. For example, in this system, the thermoplastic core blank is used in a pre-formed, hardened condition of a discrete, maximum length. As a result, some scrappage is inevitable in that both ends of the core blank, after being wrapped with the pile fabric, must be cut off to provide a functionally operative product, thus wasting both portions of the core and the pile fabric resulting from the scrapped end or ends of the otherwise completely formed product. Further, since the core blank must be heated from room temperature or other cold condition prior to application of the pile fabric in order to ensure a good bond between the core and fabric, the energy requirements are still substantial since the core blank has no residual heat.
Although proposals have been made for placing the pile fabric on a heated core, as for example in French Patent Publication 2,093,060, in which pile fabric is placed on a hot, freshly extruded core, it is believed that no such system has gone into practical use, possibly because of the difficulties associated with controlling the shrinkage variation which inevitably occurs in the matching of what is essentially a through heated core blank and a cold (i.e., room temperature, for example) pile fabric